Global Navigation Satellite Systems (GNSS) provide aircraft with navigation support in approach and landing operations. However, since the accuracy and precision requirements are high in these operations, Ground Based Augmentation Systems (GBAS) augment GNSS when an aircraft is near a GBAS Ground Subsystem. GBAS Ground Subsystems, also referred to herein as GBAS stations or ground stations, augment GNSS receivers by broadcasting pseudorange corrections and integrity information to the aircraft, which helps remove GNSS errors impacting satellite measurements processed by the aircraft's GNSS receiver. As a result, aircraft can have improved continuity, availability, and integrity performance for precision approaches, departure procedures, and terminal area operations.
A Global Navigation Satellite System (GNSS), as that term is used herein, refers to a system that utilizes a constellation of orbiting satellite for the purpose of calculating navigation and/or position solutions. Example GNSSs include, but are not limited to, the United States' Global Positioning System (GPS), Russia's Global'naya Navigatsionnaya Sputnikovaya Sisterna (GLONASS), China's Compass, the European Union's Galileo, India's Indian Regional Navigational Satellite System (IRNSS), and Japan's Quasi-Zenith Satellite System (QZSS).
One major source of error in a GNSS receiver can occur when a GNSS signal experiences delay as it passes through the ionosphere. This error can almost be completely mitigated by the GBAS station when the ionosphere is uniform between the aircraft's GNSS receiver and the GBAS station because the GBAS station and the aircraft's GNSS receiver will be experiencing similar signal delays due to uniformity of the ionosphere. However, when ionospheric disturbances produce a non-uniform ionosphere that results in differences in the delay observed by the GBAS station as opposed to the delay observed by the aircraft's GNSS receiver, the pseudorange corrections broadcast by the GBAS ground station and applied by the airborne user can result in unacceptably large position errors in the aircraft's navigation position solution. Further, conventional GBAS systems could assume that the worst case ionospheric gradient is always present and mitigate errors resulting from large ionospheric gradients using the technique of geometric screening. However, this may impact continuity and lead to loss of availability of the system.
For the reasons stated above and for other reasons stated below, it will become apparent to those skilled in the art upon reading and understanding the specification, there is a need in the art for improved systems and methods for mitigating spatial decorrelation errors caused by ionosphere delay.